The present invention relates generally to apparatus for providing a measure of the distance between the apparatus and a remote object and has particular importance in fields of distance determining and automatic focusing of, for example, photographic or television cameras.
Distance determining and automatic focusing arrangements have received considerable attention in recent years. One advantageous type of distance determining automatic focus apparatus is the spatial image correlation type. Examples of the different forms of arrangements of this type can be found in my U.S. Pat. Nos. 3,836,772, 3,838,275, 3,958,117, 4,002,899 and in U.S. Pat. No. 3,274,914 by Beterman et al.
The typical spatial image correlation apparatus includes two auxiliary optical elements (e.g., lenses or mirrors) and two detector arrays upon which images are formed by the optical elements. The object distance is determined by moving one of the auxiliary optical elements so as to change the relative position of the images on the radiation responsive detector arrays until they occupy a critical or correlation position. This position is a measure of the existing object to apparatus distance.
The relative movement of the auxiliary optical element and the detector array occurs for each distance measuring or focusing operation. The critical or correlation position occurs when there is best correspondence between the radiation distributions of two auxiliary or detection images formed on the two detector arrays. This condition of best distribution or correspondence results in a unique value or effect in the processed electrical output signals.
In most systems, a relative movement of the auxiliary optical element with respect to the detector arrays is achieved by moving a lens or mirror relative to one of the detector arrays. The particular position of the element when best distribution correspondence occurs provides a determination of the existing object apparatus distance. In an automatic focusing system, the position of the auxiliary optical element at the time of correlation is used to control the position of a primary optical element, such as a camera taking lens.
Although distance determining and automatic focusing arrangements of this type have many advantages, they also have some disadvantages. In particular, the required movement of an auxiliary optical element and the accurate determination of the position of that element when correlation occurs leads to considerable mechanical and electrical complexity. It also requires some form of motor means to provide the motion of the auxiliary optical element. This can create a problem particularly in automatic focusing cameras in which size and weight constraints are critical. The additional complexity of the requirement of some form of motor means increases the cost as well as weight and size and increases the likelihood of mechanical failure.
Several systems have been proposed that do not require scanning mirrors or lenses. For example, in my U.S. Pat. No. 3,945,023 I disclose a scheme where the outputs of detectors in two detector arrays of unequal length are compared and processed to provide an indication of the distance to the object. The primary lens is moved to a particular zone depending upon the result of this processing. In such a system for high accuracy, a relatively large number of zones is required and as a result the signal processing required for this system is also fairly large. In my copending application Ser. No. 876,972 filed Feb. 13, 1978, I disclose a system which provides for greater accuracy by combining the outputs of signals of various detectors in a predetermined manner to produce smaller size zones without decreasing the fixed detector sizes. There are, however, still size limitations that prevent the obtaining of very small zones and thus there are limits on the accuracy. In my copending application Ser. No. 696,170 filed June 14, 1976, I disclose a digital auto focus system which employs a large plurality of very small detector elements in the form of a charged couple device (CCD) or charge injection device (CID) array. In this disclosure, a first detector array receives a first detection image of the object and the second detector array receives a second detection image of the object. The second detection image is displaced by a number "n" of detectors in the second detector array with respect to the corresponding detectors of the first detector array. The number "n" is indicative of the distance between the object and the first and second detector arrays. While this system significantly increases the accuracy possible, it still requires that there be two detector arrays and two separate lenses to form paths for light from a remote object to each of the arrays. This has the effect of increasing the size, cost and complexity of the system and also makes it difficult to be used in a through-the-lens type camera.